This study of deoxycoformycin (dCF) in patients with hairy cell leukemia was written as a salvage protocol for patients who would progress or not respond to interferon in other ongoing Clinical Research Branch protocols. We also wanted to test the efficacy of this drug in T-gamma lymphoproliferative disorder since dCF had been found to have activity in other indolent T-cell diseases. Nine patients have now been treated on this protocol, five with hairy cell leukemia and four with T-gamma lymphoproliferative disorder. All patients were resistant to interferon alpha treatments and had varying degrees of peripheral blood cytopenias. Of the five patients with hairy cell leukemia, there were three partial responses, one nonresponder and one patient who died of refractory thrombocytopenia and diffuse gastrointestinal bleeding after only two doses of dCF. Of the four patients with T-gamma lymphoproliferative disorder, two have had partial responses and two were non-responders. We conclude that dCF has activity in interferon resistant hairy cell leukemia and in some patients with T-gamma lymphoproliferative disorder.